Integrated process for the production of methyl tert-butyl ether (mtbe)

Abstract

 There is provided a novel integrated process for producing methyl tertiary butyl ether from a C₄ containing hydrocarbon feedstock comprising passing the feedstock through zones of butadiene hydrogenation (4), MTBE synthesis (10), paraffin/olefin separation (18) and skeletal isomerization (26).

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a process for the production of methyl tertiary butyl ether (MTBE). More particularly, the present invention relates to a process for enhancing the ultimate yield of MTBE from a process feed stream containing a mixture of C₄ hydrocarbons.

BACKGROUND OF THE PRESENT INVENTION

[0002] In recent years, a major technical challenge to the petroleum refining industry has been the need to establish new means for producing high octane gasolines containing oxygenates in response to pollution control regulations requiring the elimination of lead from gasoline, which was previously employed as an octane enhancer. Further, the development of more efficient, higher compression ratio gasoline engines which require higher octane fuels have spurred the industry to produce new octane enhancers.

[0003] Initially, to meet these requirements, the industry developed non-lead octane boosters and reformulated high octane gasoline to incorporate increased fractions of aromatics and branched hydrocarbons. While these and other approaches were sufficient to meet the technical requirements of regulations requiring the elimination of lead, the economic impact on the cost of gasoline was significant.

[0004] Accordingly, the industry has intensified their effort to discover new processes to manufacture the gasoline products required by the marketplace. In particular, the industry has centered on blending gasoline with lower aliphatic alkyl ethers as octane enhancers. To this end, methyl tertiary butyl ether (MTBE) has been found especially useful as an octane enhancing additive. Therefore, improvements to the processes relating to the production of MTBE have become increasingly important in the petrochemical industry.

[0005] It is known that isobutylene may be reacted with methanol over an acidic catalyst to produce MTBE. Methanol is generally in ample supply, but the supply of isobutylene is limited since it is formed only in cracking operations, primarily catalytic cracking and olefins production. Since insufficient isobutylene is available from these sources to meet the growing industry needs, many C₄ production facilities based on dehydrogenation of isobutane are being used to prepare isobutylene feedstocks for MTBE production. See, e.g., Al-Muddarris, United States Patent No. 4,329,516. However, such facilities have proven very expensive to build and operate.

[0006] It would therefore represent a notable advancement in the state of the art if a process which provided for the increased production of MTBE from available feedstocks could be developed. To this end, the present inventors have developed an integrated process for the production of MTBE from readily available mixed C₄ feedstocks.

SUMMARY OF THE PRESENT INVENTION

[0007] It is an object of the present invention to provide a process for the production of methyl tertiary butyl ether.

[0008] It is another object of the present invention to enhance the ultimate yield of methyl tertiary butyl ether from a process feed stream containing a variety of C₄ hydrocarbons.

[0009] It is still another object of the present invention to provide a process for the production of methyl tertiary butyl ether which has less equipment fouling.

[0010] It is a still further object of the present invention to provide a more economic method of producing methyl tertiary butyl ether.

BRIEF DESCRIPTION OF THE DRAWING

[0011] FIGURE 1 depicts in flow chart format a preferred integrated process for the production of MTBE of the present invention.

[0012] FIGURE 2 depicts in flow chart format a process of the prior art which is employed in the comparative examples hereinbelow.

[0013] FIGURE 3 depicts in flow chart format an alternative embodiment of the integrated process for the production of MTBE of the present invention.

[0014] FIGURE 4 depicts in flow chart format an alternative embodiment of the integrated process for the production of MTBE of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0015] The present invention provides for the production of MTBE from a C₄ feedstock obtained from a catalytic cracking unit and/or an olefins production unit or mixtures thereof by conducting the following process steps, in any sequence: butadiene hydrogenation, MTBE synthesis, paraffin/olefin separation and skeletal isomerization with recycle to the MTBE synthesis or butadiene hydrogenation unit.

[0016] The present inventors have found that while each of these individual process steps are known in the art in their broadest sense, the use of these process steps in combination to produce MTBE is not taught or suggested by the prior art. Surprisingly, the present invention provides an unexpected significant increase in yield of MTBE from the C₄ feedstock. Further, in a preferred embodiment, by conducting the process steps of the present invention in the sequence of butadiene hydrogenation, MTBE synthesis, paraffin/olefin separation and skeletal isomerization, still further benefits are obtained.

[0017] However, depending upon the particular chemistry of the individual process steps, the sequence of the steps can be varied. For example, the chemistry of the skeletal isomerization step involves a number of competing reactions occurring simultaneously, such as: (1) the isomerization of butene-2 to isobutylene; (2) the isomerization of butene-2 to butene-1; (3) dimerization of butene-1 and butene-2 to various C₈ olefins; (4) transalkylation of normal butenes to produce propylene and C₅ olefins; (5) hydrogen transfer which results in the formation of n-butane; (6) polymerization which produces gasoline and distillate constituents; and (7) cracking with produces low molecular weight gas and coke. Thus, depending upon the catalyst system employed in the skeletal isomerization step, the compositional make-up of the effluent from the skeletal isomerization reactor will vary significantly. Accordingly, the integration of the various process steps can be altered to accommodate the change in chemistry in the skeletal isomerization unit.

[0018] Employing the process steps of the present invention, substantially all of the normal butene compounds are ultimately converted to MTBE, C₄ paraffins which are non-reactive, can be effectively purged from the process stream; butadienes and acetylenes are converted to butene feedstock and are eliminated upstream of the MTBE synthesis, paraffin/olefin separation and skeletal isomerization units preventing fouling and coking from occurring; and the need for employing a light ends distillation column within the skeletal isomerization unit is eliminated.

[0019] The present invention will be described in more detail hereinbelow with reference to a preferred sequence of process steps. However, it is to be understood that other sequences of process steps may be employed in the practice of the present invention.

[0020] Referring to FIG. 1, a C₄ feedstock in a line 2 is first fed to a hydroisomerization unit 4. Alternatively, the hydroisomerization unit can comprise any butadiene hydrogenation unit known to those of ordinary skill in the art which converts butadiene to butenes, such as a hydroisomerization unit or selective hydrogenation unit. Preferred is a hydroisomerization unit which in addition to converting butadiene to butenes also isomerizes at least a portion of the butene-1 component to the butene-2 components. The hydroisomerization unit 4 is fed with hydrogen by a line 6. The C₄ feedstock is typically a mixed C₄ feedstock from either a catalytic cracking or olefins production process, or mixtures thereof, and which comprises all of the C₄ isomers (acetylenes, dienes, olefins and paraffins), and small quantities of C₃ and C₅ hydrocarbons. The C₄ isomers are as follows; ethyl acetylene, vinyl acetylene, 1,3-butadiene, 1,2-butadiene, isobutylene, cis-2-butene, trans-2-butene, 1-butene, isobutane and n-butane. The actual composition of the C₄ stream will vary considerably between cracking and olefin sources and will also differ if a butadiene extraction unit is employed upstream to recover butadiene from olefins feedstock.

[0021] In the hydroisomerization unit 4, most of the acetylenes and dienes are catalytically converted to butenes and most of the 1-butene is catalytically converted to the 2-butenes, i.e., cis-2-butene and trans-2-butene, in the presence of hydrogen.

[0022] Hydroisomerization is a process which is well known to those of ordinary skill in the art and any particular hydroisomerization process may be employed. Typically, the hydroisomerization step is carried out in the presence of a catalyst comprising at least one hydrogenating metal and a moderately acidic carrier. A preferred catalyst can comprise a Group VIII metal, such as platinum, palladium and/or nickel, on a microporous crystalline silicate, such as a mordenite with a surface area of from 100 to 800 m²/g.

[0023] Suitable hydroisomerization conditions may include a temperature of from 40° to 400°C, a pressure from 1-100 bar and a space velocity from 0.5 to 20 kg hydrocarbon feed/kg catalyst hour. Preferred conditions are a mixed phase process at a temperature of from 40° to 150°C, a pressure of from 10 to 40 bar and a space velocity of from 1 to 15 kg feed/kg catalyst hour. See, e.g., Grandvallet et al., United States Patent No. 5,023,389.

[0024] The effluent stream 8 from the hydroisomerization unit 4 substantially comprising isobutylene, cis-2-butene, trans-2-butene, isobutane, n-butane, unconverted 1-butene and C₃ and C₅ components is combined with recycle stream 28, described hereinbelow, and directed to an MTBE synthesis unit 10.

[0025] The synthesis of methyl tertiary butyl ether (MTBE) from isobutylene and methanol is a process which is well known to those of ordinary skill in the art and any particular synthesis process may be employed in the practice of the present invention. The general reaction scheme is set forth below.


Typically, the synthesis step is carried out at mild temperatures, in the liquid phase, in the presence of a sulfonated polystyrene resin. See, Hatch and Matar, "From Hydrocarbons to Petrochemicals," Gulf Publishing Co., 1981, pp. 128-29.

[0026] The reaction usually employs an acid type ion exchange resin, such as a high molecular weight carbonaceous material containing sulfonate groups -SO₃H. Sulfonated resins of various types are available such as the sulfonated coals, phenol formaldehyde resins reacted with sulfuric acid, sulfonated resinous polymers of cumarone-indene with cyclopentadiene, strongly acidic cationic exchange resins such as sulfonated divinylbenzene polystyrene copolymers, and others, under various commercial names. The catalyst can be employed in a particulate solid form with sizes ranging from about 10 to about 50 U.S. sieve employing about 0.5 to 50 percent dry weight of catalyst relative to liquid content of the reactor. A fixed bed of particulate solid ion exchange resin catalyst, e.g., such as Amberlyst 15 from Rohm & Haas Co., or Dowex® M31 or M32 from Dow Chemical Co., may be employed. The same catalyst may also be employed in tubular reactors or supported in bags or other devices which permit catalytic distillation to be practiced in the reactor.

[0027] The reaction of the isobutylene with methanol can be carried out under any suitable reaction conditions. The mole ratio of methanol to isobutylene generally is in the range of about 0.05 to 10, preferably about 0.1 to 5, and still more usually about 1 to 1, at a temperature in the range of about 100°F to about 250°F, more usually about 100°F to 250°F, employing a pressure sufficient to maintain the reactants substantially in the liquid state, typically in the range of about 80 to 400 psig. The liquid hourly space velocity, volume of feed per volume of catalyst per hour, is preferably about 0.5 to 10.

[0028] More specific processes of MTBE synthesis are described in Childs, United States Patent No. 4,440,963, Wentzheimer et al., United States Patent No. 4,198,530, Masilamani et al., United States Patent No. 4,792,639, Smith, Jr. et al., United States Patent No. 4,950,803, Lee, United States Patent No. 3,946,450 and Leum et al., United States Patent No. 2,480,940.

[0029] The resultant product MTBE, along with the C₅ and heavier components, are withdrawn from the MTBE unit through a line 14 by fractionation, as is well known to those skilled in the art. The remaining components of the MTBE synthesis feed, the cis-2-butene, trans-2-butene, isobutane, n-butane, unconverted 1-butene and C₃ components are then directed through a line 16 to a paraffin/olefin separation unit. The paraffin/olefin separation can be carried out by a wide variety of separation processes known to those skilled in the art, including, but not limited to, extractive distillation, selective membrane separation and/or molecular sieve separation. Particularly suitable for use in the practice of the present invention is an extractive distillation unit 18 to remove paraffins and C₃ components.

[0030] Extractive distillation is a well known process, and has been employed in the past to separate butadiene from C₄ feedstreams, as well as other separations such as separating MTBE from cyclopentane. See, e.g., Berg, United States Patent No. 4,661,209. Extractive distillation generally refers to processes where a higher boiling selective solvent is added to alter the relative volatilities of the components in the feed mixture. See, generally, Perry and Chilton, "Chemical Engineers' Handbook," McGraw Hill, 5th ed., 1973, pp. 13-43 to 13-48.

[0031] A wide variety of solvents may be employed in the extractive distillation step of the present invention, including, but not limited to, tetrahydrofuran, diethyl ketone, diethyl carbonate, methyl ethyl ketone, pentanedione, cyclopentanone, acetone, butyronitrile, acetyl piperidine, acetophenone, pyridine, diethyl oxalate, propionitrile, dimethyl acetamide, n-methyl pyrrolidone, acetonyl acetone, tetrahydrofurfuryl alcohol, dimethyl sulfolane, dimethyl cyanamide, methyl carbitol, dimethyl formamide, methyl cellosolve, furfural, acetonitrile, ethylene chlorhydrin, gamma-butyrolactone, methanol, beta-chloropropionitrile, pyrrolidone, propylene carbonate, nitromethane, ethylene diamine and mixtures of any of the foregoing. Especially preferred is acetonitrile. Further, these solvents may also be employed with a water diluent.

[0032] The solvent, in a line 20, is introduced near the top of the extractive distillation column or tower (not shown), usually a few plates from the top, and flows downward until it reaches the stillpot or reboiler. Its presence on each plate of the distillation column alters the relative volatility of the close boiling compounds to make the separation on each plate greater than would be possible without the solvent and thus requires either fewer plates to effect the same separation, makes possible a greater degree of separation with the same number of plates and also makes possible separation which could not be achieved with conventional distillation.

[0033] The light compounds, C₃ and lighter boiling hydrocarbons, as well as the C₄ paraffins isobutane and n-butane, are thereby removed from the top of the extractive distillation unit through a line 22. The bottoms from the extractive distillation are directed to a stripper (not shown) wherein the cis-2-butene, trans-2-butene and unconverted 1-butene are recovered from the overhead of the stripper, withdrawn through a line 24 and fed to the skeletal isomerization unit 26.

[0034] Skeletal isomerization is a process by which the 2-butenes, cis-2-butene and trans-2-butene, are converted to isobutylene and the 1-butene is isomerized to a 2-butene and which can then be further isomerized to isobutylene. Skeletal isomerization of olefins is known to be conducted by contacting unbranched olefins with acidic catalysts at pressures near atmospheric and temperatures ranging from about 600 to 1100°F. The isomerization of olefins is well known to be limited by the thermodynamic equilibrium of reacting species. Useful catalysts and processes are described in the patent literature, inter alia, Smith, Jr., United States Patent No. 4,482,775, Sun, United States Patent No. 4,778,943, Schwerdtel et al., United States Patent No. 4,548,913, Del Rossi et al., United States Patent No. 5,107,047 and Chih-Cheng, et al., EP 0 508 008.

[0035] Accordingly, a portion of the 2-butenes are essentially converted to isobutylene with a small amount of light and heavy hydrocarbon by-products (gasoline) and the effluent from the skeletal isomerization unit is recycled in a line 28 to the MTBE synthesis unit for conversion of the isobutylene to MTBE product. Further, the heavy hydrocarbon by-products (gasoline) can be withdrawn from the skeletal isomerization unit through a line 29.

[0036] When a relatively minor quantity of heavy hydrocarbon (gasoline) by-product is produced in the skeletal isomerization unit the heavy hydrocarbon takeoff stream 29 can be omitted and the heavy hydrocarbon can be recycled with the rest of the effluent from the skeletal isomerization unit in streams 28 to the hydroisomerization (see Figure 4) or MTBE synthesis unit where it can be purged or removed from the process with the methyl tertiary butyl ether product stream 14.

[0037] By employing the integrated process of the present invention, significant advantages are achieved over the teachings of the prior art. See Fig. 2. By employing the process of the present invention, catalyst fouling in the MTBE synthesis step is reduced by upstream butadiene conversion to butenes, the capital and operating costs of the extractive distillation step are reduced since the 2-butene components require less trays and utilities to effect the equivalent separation than 1-butene, fouling in the extractive distillation unit is reduced due to upstream conversion of butadiene, and the overall yield of the process is improved since additional isobutylene is available for conversion. The process of the present invention enables an operator to convert from about 80 to about 90% or greater of the entire raw C₄ stream derived from ethylene production plant to MTBE. Additionally, the removal of C₅ and heavier components in the MTBE synthesis step prevents contamination, and facilitates recovery, of the extractive solvent in the extractive distillation unit.

[0038] Further, there is no need for including a depropanizer in the skeletal isomerization process to remove light by-products. These light ends are inert in the MTBE synthesis and are removed in the extractive distillation overhead. The heavy hydrocarbon by-products (gasoline) are removed from the process stream in the MTBE product stream or via a takeoff in the skeletal isomerization unit.

[0039] Alternatively, as shown in Fig. 3, it is contemplated that the process of the present invention provides for a by-pass of a portion of the hydrocarbon feed around the extractive distillation unit. For ease of understanding, the parts of the process of Fig. 3 have been given part numbers similar to the corresponding parts of the process of Fig. 1, except in the 100 series. The use of a by-pass line 130 around the extractive distillation unit 118 results in the feed line 124 to the skeletal isomerization unit 126 comprising both the bypass stream 130 and the olefin enriched stream 123 from the extractive distillation unit.

[0040] The sequence of Fig. 3, comprising a by-pass of the extractive distillation with a portion of the MTBE synthesis effluent, is particularly useful in embodiments where the feed to the integrated MTBE process contains low concentrations of normal and isobutane. With low concentrations of normal and isobutane in the feed, it is desirable to by-pass the extractive distillation with a portion of the effluent from the MTBE synthesis unit since the paraffin purge stream is relatively small compared to the quantity of material to be processed. Moreover, the use of the by-pass results in an increase in MTBE product. Olefin loss in the extractive distillation unit from olefins in the by-pass stream is avoided and the additional olefins are then converted to MTBE.

[0041] Another alternative embodiment is shown in Fig. 4. For ease of understanding, the parts of the process of Fig. 4 have been given part numbers similar to the corresponding parts of the process of Fig. 3, including an optional by-pass stream, except in the 200 series. The process of Fig. 4 comprises directing the recycle stream 228 from the skeletal isomerization unit 226 to the feed stream 202 of the hydroisomerization unit 204. This embodiment is particularly useful where the skeletal isomerization catalysts isomerize a significant portion of the butene-2 hydrocarbons to butene-1. By recycling the effluent from the skeletal isomerization unit to the hydroisomerization unit, additional butene-2 is provided for the extractive distillation unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] The following examples illustrate the present invention. They are not to be construed to limit the scope of the appended claims in any manner whatsoever.

EXAMPLE

[0043] Material balances were performed on a process according to the present invention comprising, in sequence, a hydroisomerization unit (operating at 77.8% conversion), an MTBE synthesis unit, an extractive distillation unit and a skeletal isomerization unit (operating at 37.4 % n-butene conversion). For comparative purposes, processes without the extractive distillation, but with 15, 30 and 60% purge, respectively, were also analyzed. The results are set forth below in Tables 1-4. All values are reported in kg/hr.

[0044] In Tables 2-4, the primed stream numbers generally correspond to the stream numbers in Figure 1. Further, stream no. 22' refers to a purge stream removed from the MTBE synthesis unit effluent which includes both paraffins and valuable olefins; stream no. 24' refers to the stream which is fed to the skeletal isomerization unit and comprises the MTBE synthesis effluent minus the purge stream 22'; stream 27' refers to a light hydrocarbon takeoff from the skeletal isomerization unit; and stream 29' refers to a heavy hydrocarbon (gasoline) takeoff from the skeletal isomerization unit. Additionally, unit 4' is normally a selective hydrogenation unit which would convert butadiene to olefins but would not perform the olefin isomerization. See Figure 2.

[0045] For convenience, the results of the material balances are summarized below in Table 5.

TABLE 5

Summary of Results
Process	MTBE Produced	MTBE Feed	SI Feed
Table 1 - with extractive distillation	22488	40809	21738
Table 2 - 15% Purge	19900	53508	34665
Table 3 - 30% Purge	17606	37682	18490
Table 4 - 60% Purge	14738	26419	6791
SI - Skeletal Isomerization

[0046] From Table 5 it can be seen that the process according to the appended claims with the extractive distillation unit provides significant advantages over the processes without the extractive distillation step. As compared to the process employing the 15% purge, the process of the present invention provides improved yields of MTBE and significantly reduces the feed to the MTBE synthesis unit and skeletal isomerization unit. As compared to the process with the 30% purge, while the feed rates to the MTBE synthesis and skeletal isomerization units are similar to the process of the present invention, the process of the present invention provides a significant increase in MTBE yield. Further, as compared to the process with the 60% purge, while the 60% purge process has reduced feed rates to the MTBE synthesis unit and the skeletal isomerization unit, the MTBE yield for the 60% purge process is only abut 66% of the MTBE yield of the present process.

[0047] Accordingly, it can be seen that the process of the present invention concurrently provides both increased yields and reduced feed rates to the MTBE synthesis and skeletal isomerization units.

[0048] Many variations of the present invention will suggest themselves to those skilled in the art in light of the above-detailed description. For example, the specific conditions and catalysts for each of the process steps may be varied. Further, molecular sieve separation and selective membrane separation units may be employed in place of or in addition to the extractive distillation unit; and selective hydrogenation units may be employed in place of or in addition to the hydroisomerization unit. All such obvious modifications are within the full intended scope of the appended claims.

[0049] All of the above-referenced patents and publications are hereby incorporated by reference.

Claims

1. An integrated process for the production of methyl tertiary butyl ether comprising passing a hydrocarbon feedstock containing C₄ components through zones of butadiene hydrogenation, methyl tertiary butyl ether synthesis, paraffin/olefin separation and skeletal isomerization.

2. A process as defined in Claim 1 wherein said C₄ containing feedstock comprises ethyl acetylene, vinyl acetylene, 1,3-butadiene, 1,2-butadiene, isobutylene, cis-2-butene, trans-2-butene, 1-butene, isobutane, n-butane and mixtures of any of the foregoing.

3. A process as defined in Claim 2 wherein said C₄ containing feedstock is a portion of the effluent from a fluid catalytic cracking process.

4. A process as defined in Claim 2 wherein said C₄ containing feedstock is a portion of the effluent from an olefins production plant.

5. A process as defined in Claim 1 which further comprises an upstream butadiene extraction unit.

6. A process as defined in Claim 1 wherein said butadiene hydrogenation comprises a hydroisomerization and/or a selective hydrogenation.

7. A process as defined in Claim 6 wherein said butadiene hydrogenation comprises hydroisomerization.

8. A process as defined in Claim 7 wherein said hydroisomerization comprises catalytically converting acetylenes and dienes to butenes, and catalytically converting 1-butene to 2-butenes.

9. A process as defined in Claim 8 wherein the catalyst for the hydroisomerization comprises at least one hydrogenating metal and a moderately acidic carrier.

10. A process as defined in Claim 9 wherein said hydrogenating metal comprises platinum, palladium and/or nickel.

11. A process as defined in Claim 8 wherein said hydroisomerization is carried out at a temperature ranging from about 40°C to about 400°C, a pressure ranging from about 1 to about 100 bar and a space velocity ranging from about 0.5 to 20 kg hydrocarbon feed/kg catalyst hour.

12. A process as defined in Claim 11 wherein the hydroisomerization is carried out in a mixed phase at a temperature ranging from about 40° to about 150°C, a pressure ranging from about 10 to about 40 bar and a space velocity ranging from about 1 to about 15 kg feed/kg catalyst hour.

13. A process as defined in Claim 1 wherein said methyl tertiary butyl ether synthesis comprises the liquid phase reaction of isobutylene with methanol in the presence of an acid type ion exchange resin.

14. A process as defined in Claim 13 wherein said acid type ion exchange resin is selected from sulfonated coals, phenol formaldehyde resins reacted with sulfuric acids, sulfonated resinous polymers of cumaroneindene with cyclopentadiene, sulfonated divinylbenzene polystyrene copolymers and mixtures of any of the foregoing.

15. A process as defined in Claim 14 wherein said acid type ion exchange resin comprises a sulfonated divinylbenzene polystyrene copolymer.

16. A process as defined in Claim 13 wherein said methyl tertiary butyl ether synthesis is carried out at a mole ratio of methanol to isobutylene of from about 0.05 to 10 and a temperature ranging from about 60°F to about 300°F and a pressure ranging from about 80 to 400 psig.

17. A process as defined in Claim 16 wherein said synthesis is carried out at a mole ratio ranging from about 0.1 to about 5 and a temperature ranging from about 100°F to about 250°F.

18. A process as defined in Claim 1 wherein said paraffin/olefin separation comprises separating paraffins from olefins by extractive distillation, selective membrane separation and/or molecular sieve separation.

19. A process as defined in Claim 18 wherein said paraffin/olefin separation comprises extractive distillation.

20. A process as defined in Claim 19 wherein the solvent, optionally in the presence of a water diluent, for the extractive distillation step is selected from tetrahydrofuran, diethyl ketone, diethyl carbonate, methyl ethyl ketone, pentanedione, cyclopentanone, acetone, butyronitrile, acetyl piperidine, acetophenone, pyridine, diethyl oxalate, propionitrile, dimethyl acetamide, n-methyl pyrrolidone, acetonyl acetone, tetrahydrofurfuryl alcohol, dimethyl sulfolane, dimethyl cyanamide, methyl carbitol, dimethyl formamide, methyl cellosolve, furfural, acetonitrile, ethylene chlorhydrin, gamma-butyrolactone, methanol, beta-chloropropionitrile, pyrrolidone, propylene carbonate, nitromethane, ethylene diamine and mixtures of any of the foregoing.

21. A process as defined in Claim 20 wherein said solvent comprises acetonitrile, optionally in the presence of a water diluent.

22. A process as defined in Claim 1 wherein said skeletal isomerization step is carried out in the presence of an acidic catalyst, at a pressure of about atmospheric and temperatures ranging from about 600°F to about 1100°F.

23. A process as defined in Claim 1 wherein the effluent from the zone of skeletal isomerization is fed to the zone of methyl tertiary butyl ether synthesis.

24. A process as defined in Claim 1 wherein the effluent from the zone of skeletal isomerization is fed to the zone of butadiene hydrogenation.

25. An integrated process for the production of methyl tertiary butyl ether from a C₄ containing feedstock comprising the following process steps conducted in sequence:

(a) butadiene hydrogenation;

(b) methyl tertiary butyl ether synthesis;

(c) paraffin/olefin separation; and

(d) skeletal isomerization.

26. A process as defined in Claim 25 wherein said C₄ containing feedstock comprises ethyl acetylene, vinyl acetylene, 1,3-butadiene, 1,2-butadiene, isobutylene, cis-2-butene, trans-2-butene, 1-butene, isobutane, n-butane and mixtures of any of the foregoing.

27. A process as defined in Claim 26 wherein said C₄ containing feedstock is a portion of the effluent from a fluid catalytic cracking process.

28. A process as defined in Claim 26 wherein said C₄ containing feedstock is a portion of the effluent from an olefins production plant.

29. A process as defined in Claim 25 which further comprises an upstream butadiene extraction unit.

30. A process as defined in Claim 1 wherein said butadiene hydrogenation comprises hydroisomerization and/or selective hydrogenation.

31. A process as defined in Claim 30 wherein said butadiene hydrogenation comprises hydroisomerization.

32. A process as defined in Claim 31 wherein said hydroisomerization comprises catalytically converting acetylenes and dienes to butenes, and catalytically converting 1-butene to 2-butenes.

33. A process as defined in Claim 32 wherein the catalyst for the hydroisomerization comprises at least one hydrogenating metal and a moderately acidic carrier.

34. A process as defined in Claim 33 wherein said hydrogenating metal comprises platinum, palladium and/or nickel.

35. A process as defined in Claim 34 wherein said hydroisomerization is carried out at a temperature ranging from about 40°C to about 400°C, a pressure ranging from about 1 to about 100 bar and a space velocity ranging from about 0.5 to 20 kg hydrocarbon feed/kg catalyst hour.

36. A process as defined in Claim 35 wherein the hydroisomerization is carried out in a mixed phase at a temperature ranging from about 40° to about 150°C, a pressure ranging from about 10 to about 40 bar and a space velocity ranging from about 1 to about 15 kg feed/kg catalyst hour.

37. A process as defined in Claim 25 wherein said methyl tertiary butyl ether synthesis comprises the liquid phase reaction of isobutylene with methanol in the presence of an acid type ion exchange resin.

38. A process as defined in Claim 37 wherein said acid type ion exchange resin is selected from sulfonated coals, phenol formaldehyde resins reacted with sulfuric acids, sulfonated resinous polymers of cumaroneindene with cyclopentadiene, sulfonated divinylbenzene polystyrene copolymers and mixtures of any of the foregoing.

39. A process as defined in Claim 38 wherein said acid type ion exchange resin comprises a sulfonated divinylbenzene polystyrene copolymer.

40. A process as defined in Claim 37 wherein said methyl tertiary butyl ether synthesis is carried out at a mole ratio of methanol to isobutylene of from about 0.05 to 10 and a temperature ranging from about 60°F to about 300°F and a pressure ranging from about 80 to 400 psig.

41. A process as defined in Claim 40 wherein said methyl tertiary butyl ether synthesis is carried out at a mole ratio ranging from about 0.1 to about 5 and a temperature ranging from about 100°F to about 250°F.

42. A process as defined in Claim 37 wherein there is recovered a product stream comprising methyl tertiary butyl ether and a synthesis effluent stream comprising cis-2-butene, trans-2-butene, isobutane, 1-butene and n-butane.

43. A process as defined in Claim 25 wherein said paraffin/olefin separation comprises separating paraffins from olefins by extractive distillation, selective membrane distillation and/or molecular sieve separation.

44. A process as defined in Claim 43 wherein paraffin/olefin separation comprises extractive distillation.

45. A process as defined in Claim 44 wherein the solvent, optionally in the presence of a water diluent, for the extractive distillation step is selected from tetrahydrofuran, diethyl ketone, diethyl carbonate, methyl ethyl ketone, pentanedione, cyclopentanone, acetone, butyronitrile, acetyl piperidine, acetophenone, pyridine, diethyl oxalate, propionitrile, dimethyl acetamide, n-methyl pyrrolidone, acetonyl acetone, tetrahydrofurfuryl alcohol, dimethyl sulfolane, dimethyl cyanamide, methyl carbitol, dimethyl formamide, methyl cellosolve, furfural, acetonitrile, ethylene chlorhydrin, gamma-butyrolactone, methanol, beta-chloropropionitrile, pyrrolidone, propylene carbonate, nitromethane, ethylene diamine and mixtures of any of the foregoing.

46. A process as defined in Claim 45 wherein said solvent comprises acetonitrile, optionally in the presence of a water diluent.

47. A process as defined in Claim 44 wherein said extractive distillation step comprises a tower which separates the synthesis effluent into an overhead purge stream comprising C₃ and lighter boiling hydrocarbons, isobutane and n-butane and a stripper effluent stream comprising mostly cis-2-butene, trans-2-butene and 1-butene.

48. A process as defined in Claim 44 further comprising by-passing a portion of the synthesis effluent around the extractive distillation step.

49. A process as defined in Claim 25 wherein said skeletal isomerization step is carried out in the presence of an acidic catalyst, at a pressure of about atmospheric and temperatures ranging from about 600°F to about 1100°F.

50. A process as defined in Claim 47 wherein the effluent from the skeletal isomerization step comprises isobutylene, cis-2-butene, trans-2-butene and 1-butene.

51. A process as defined in Claim 50 wherein the effluent from the skeletal isomerization step is recycled to the zone of methyl tertiary butyl ether synthesis.

52. A process as defined in Claim 50 wherein the effluent from the skeletal isomerization step is recycled to the butadiene hydrogenation step.

53. A process as defined in Claim 52 wherein said butadiene hydrogenation step comprises hydroisomerization.

Drawing